1. Field of the Invention
This invention relates to gas turbine apparatus for electric power generation, in particular relates to gas turbine apparatus which can uses low quality oil such as heavy oil, residue oil and the like, or coal as fuel.
2. Description of the Prior Arts
These days, from the point of view of fuel resources and environment problems, diversification of the fuels for high temperature apparatus such as a gas turbine and the like is aggressively promoted. Since, among various fuels, so-called low quality oil such as heavy oil, residue oil which is left at the final stage of petroleum refining process, or orimulsion and the like is limited in their usage, a large quantity of them is left unused. Thus, they are not expensive in their cost and expected inevitably to increase in their supply amount as demand for high quality oil such as lamp oil increases in future. From the above circumstances, the low quality oils are expected to be alternative for high quality oils such as LNG, lamp oil, light oil, and the like.
In FIG. 19, an example of a structure of a conventional heavy oil fired gas turbine system is shown. Air taken in through an air inlet 1, after being compressed by an air compressor 2, is mixed/burned in a combustion chamber 3 with fuel supplied from a fuel tank 4. High temperature and high speed combustion gas generated by burning the fuel is sent to a gas turbine 5 which possesses a plurality of stages of a combination of a turbine rotor blade and a turbine stator blade (hereinafter referred to as rotor.stator blade).
The above described combustion gas is at first transferred to the first stage 5a of the rotor.stator blade and the energy of the combustion gas is transformed into a rotation movement of the turbine rotor blade. Further, the combustion gas, by sequentially going through the second stage 5b, the third stage 5c of the rotor.stator blade, drives the turbine rotor blade of each stage. The rotation torque obtained by each turbine rotor blade is transmitted to an electric generator 6, the electric generator driven thereby. These principal structures are common for all general type gas turbine systems including heavy oil, LNG, and lamp oil fired one.
Now, since, in the low quantity oil (heavy oil, lamp oil and so on), impurities such as V, Na, K, Pb, S and the like are included much in quantity, corrosion of the high temperature member by these impurities is serious. Therefore, when the low quality oil is used, pretreatment of the fuel is indispensable. For the heavy oil fired gas turbine system, a mechanism 7 for pretreatment of the fuel is accompanied.
In FIG. 20, an example of the construction of the fuel pretreatment mechanism 7 for the conventional heavy oil fired gas turbine system is shown. The heavy oil supplied from a fuel tank 4 and pure water supplied from a tank 8 are mixed and centrifuged with a centrifugal machine 9, thereby water soluble corrosive elements such as Na, K, and the like are eliminated. Among the erosive elements, since V is not easily soluble in water, the centrifugal method with water can not eliminate V. Therefore, when the fuel is transferred to the gas turbine 5 through a fuel transferring pump 10, V corrosion suppressing agent is added from a corrosion suppressing agent tank 11. With addition of the V corrosion suppressing agent, the V corrosion of the high temperature member of the gas turbine 5 is aimed to be reduced. As the V corrosion suppressing agents, a mixture of Mg compound such as MgSO.sub.4 or Si compound with water or solvent can be used.
However, in the above described conventional gas turbine system, at the stage such as the first stage 5a of the gas turbine 5 which is exposed to high temperature combustion gas, reaction products such as MgSO.sub.4, Mg.sub.3 V.sub.2 O.sub.8, MgO and the like are heavily deposited on the blade portion, where the reaction products are formed between the Mg added as the V corrosion suppressing agent and elements included in the combustion gas atmosphere. This causes output power decrease due to the decrease of area of gas flow path and material deterioration accompanying temperature rise due to narrowing of the cooling hole.
To remedy these problems, by adding solid particles in the combustion gas, the deposited reaction products on the blade are mechanically removed. Or, when the system is stopped running, chemical cleaning with water or chemicals is executed. In FIG. 21, a representative structure of wet cleaning apparatus is shown. This apparatus is equipped with a mechanism for cleaning the inside of the combustion chamber 3 or the gas turbine 5 by sending in the pure water from the pure water tank 12 through a pump 13. However, such frequent cleanings of the gas turbine lead to lowering of availability ratio of the gas turbine system. Even if the above described cleaning procedure is executed, basically it is required to prevent the reaction products from precipitating. Therefore, presently, the inlet temperature of the gas turbine is limited only at the lower temperature side.
Further, in the case of a gas turbine system which uses the fuels such as the low quality oil, coal, and the like, problem is sulphidizing corrosion due to sulfur included in the fuel is pointed out. That is, due to the reaction between sulfur and Ni and the like included in the superalloy which constitutes the base material of the high temperature member, the reaction products are formed. Since the melting points of the compounds are low, liquid phase due to sulfide is formed at the tip end of corrosion. This selectively corrodes grain boundary and make rapidly lower the strength of the base material. The protective oxide film formed on the surface of the superalloy loses the protective effect when melted salt such as Na.sub.2 SO.sub.4 and the like which are deposited on its surface are dissolved. Thereby, rapid lowering of the strength of the base material occurs. To prevent sulphidizing corrosion, although prevention of corrosion is conventionally executed by employing high Cr superalloy corrosion resistant coating, sufficient preventive effect can not be obtained.
As described above, in the conventional gas turbine apparatus, gas obtained by burning the fuel, in which the V corrosion suppressing agent is added, is directly sent into the gas turbine. Around the first stage of the rotor.stator blade which temperature becomes high, the reaction products (ash content) mainly consisting of Mg which is included particularly in the V corrosion suppressing agent precipitate, thereby causes narrowing of the path of gas flow to result in lowering of the output power or causes closing of the cooling holes to result in serious deterioration of materials. The deposition of the reaction products due to the V corrosion suppressing agent restricts the temperature range where the gas turbine can be operated. This prevents the gas turbine from operating efficiently at turbine inlet temperature of, for example, 1,473 K or more. Further, when such fuel as the low quality oil or coal both abundant in sulfur content is used, there appears the sulphidizing corrosion at the rotor.stator blade of the gas turbine due to the sulfur. This is one factor determining the life of the gas turbine.
From above explained reasons, in the conventional gas turbine apparatus, it is a subject to, while suppressing the corrosion of the high temperature member due to V, suppress the deposition of the reaction products due to the V corrosion suppressing agent. Further, it is also a subject to suppress the corrosion of the high temperature member due to sulfur. Thus, it is required, by remedying these, to improve the system availability ratio and to realize long life of the gas turbine, further to improve efficiency due to utilization of higher temperature of the fuel gas.